Freezers wherein a conveyor belt or the like transports food through a low-temperature chamber are well known in the art. As described in copending application No. 373,056, now U.S. Pat. No. 4,953,365 the disclosure of which is incorporated herein by reference, cooling of food product in such freezers is generally accomplished either by a cryogen spray or by circulation of air or other gas over the evaporator coil of a mechanical refrigeration unit.
Mechanical refrigeration for the food processing industry has generally been supplied by systems using ammonia or chloro-fluoro-carbons or chloro-fluorohydrocarbons ("CFC's/HCFC's"), e.g., R12, R22, or R502, as refrigerants in single or multi-stage systems. The refrigerant used is normally dependent on system size, cost, and expected operating conditions. Large systems, i e., those having capacities of 50 tons of refrigeration (TR) and over, typically use ammonia as the refrigerant. Smaller systems, under 50 TR, generally use CFC's/HCFC's due to cost of equipment and simplicity. For certain applications, mechanical refrigeration is preferred to cryogen injection. However, conventional mechanical refrigeration systems have disadvantages due to their use of ammonia and CFC's/HCFC's. In a food freezer plant environment, leakage of even small amounts of ammonia is annoying to workers, and large concentrations of ammonia in a worker's environment impose a health hazard. CFC's/HCFC's have higher exposure limits, but some have been found to be harmful to the environment.
It is a general object of the invention to provide a food freezer having an improved mechanical refrigeration system. Further objects and advantages of the invention will become apparent from the description set forth below and the accompanying drawing.